The present invention relates to a magnetoresistive (MR) head, a manufacturing method thereof, a magnetic reading/writing apparatus using the head, and a magnetoresistive (MR) sensor.
The following patent documents are referred to below by ordinal number, and are hereby incorporated by reference:
1. U.S. Pat. No. 5,159,513;
2. U.S. Pat. No. 5,583,725;
3. JP-A No. 2000-113418; and
4. JP-A No. 2000-20926.
In recent years, spin valve type magnetoresistive sensors have been used as the writing sensor in high density magnetic recording apparatuses. The spin valve sensor is disclosed in Patent Document 1 is an example.
The essential feature of the spin valve type magnetoresistive sensor is the basic constitution comprising a ferromagnetic film referred to as a pinned layer, a ferromagnetic soft magnetic layer referred to as a free layer, a conductive layer put between the two layers adjacent directly thereto, and an exchange coupling film in direct contact with the pinned layer (that is, a multi-layered constitution in the order of free layer, conductive layer, pinned layer and exchange coupling film) in which an anti-ferromagnetic material is usually used for the exchange coupling film. Further, the magnetoresistive sensor has electrodes for supplying current to the layers and a longitudinal bias layer for applying a longitudinal bias magnetic field for suppressing noises referred to as Barkhausen Noise caused by non-uniformity of the free layer magnetization. Usually, a Co-based permanent magnetic film is used for the longitudinal bias layer. The sensor is usually disposed in a minute space called a magnetic gap put between two ferromagnetic bodies referred to as magnetic shields and reads magnetization signals from a recording medium with high-resolution.
Magnetization of the pinned layer is fixed in a direction perpendicular to the recording medium opposed surface (magnetic head air bearing surface), that is, the pinned layer does not change its magnetization direction relative to the magnetic field of the medium and the magnetic field applied to the sensor film during reading. Magnetization in the free layer changes its direction in accordance with the magnetic field from the receding medium to cause a change in magnetic resistance due to a change formed in the angle between the magnetization of the pinned layer and the magnetization of the free layer. Generation of the resistance change as the signal is an operation principle of the spin valve type head.
The exchange coupling film is adjacent to the pinned layer and gives a strong bias magnetic field to the pinned layer. Since the magnetization of the pinned layer is fixed by the bias magnetic field, the magnetization direction is not changed by the magnetic field from the recording medium or the magnetic field from the recording head. An anti-ferromagnetic material is usually used for the exchange coupling film, and it is necessary that the exchange coupling magnetic field applied to the pinned layer is sufficiently large within the range of the operation temperatures of the sensor. To this end, a regular PtMn alloy having 1:1 platinum and manganese composition is commonly used.
Patent Documents 2 and 3 disclose a proposal for a constitution not having the exchange coupling film adjacent to the pinned layer.
The magnetoresistive sensor film is exposed to the medium opposed surface of the magnetic head for effectively sensing the magnetic field from magnetic bits recorded in the medium. In addition, the thus exposed magnetoresistive film is covered with an ABS protective film. To make the magnetic head in this constitution, the process for the constitution is divided into a step of forming devices on a substrate and a slider fabrication step of cutting out individual devices from the substrate on which devices are formed and fabricating each of them into a shape suitable for allowing it to fly above the recording medium, referred to as a slider. In the slider fabrication step, the substrate is cut out by machining into blocks called bars, in smaller units, each having a plurality of devices. The bar is polished by a polishing step referred to as a computer lapping to expose the magnetoresistive sensor to the medium opposed surface. The step is referred to as an air bearing surface fabrication step.
Further, Patent Document 4 discloses various results of studies of concrete constitution of a stacked pinned layer.
To achieve high recording density of 100 GB/in2 class, it is necessary to miniaturize the magnetoresistive sensor film and miniaturization to about 0.1 μm track width×0.1 μm sensor height has been tried. The sensor height is a width in the direction perpendicular to the medium opposed surface of the sensor film. A significant problem in the course of miniaturization is that the pinned layer of the sensor film suffers from damage during air bearing surface fabrication for the sensor height to a size of 0.1 μm. The damage of the pinned layer is encountered in a region of 30 to 50 nm from the air bearing surface; if the sensor height is 0.1 μm (100 nm), 30 to 50% thereof are damaged. As a result, the change of the magnetic resistance of the sensor film is 30 to 50% of the value intended. Accordingly, the read signal is decreased by 30 to 50% while reading the recorded information of the medium and the information is read inaccurately.
As recording density is further increased, the sensor height will be further miniaturized and the problem will become more severe. Where the sensor height is 50 nm or less, the entire area of the sensor film can be damaged and the change in resistance of the sensor film can scarcely be obtained and, accordingly, this problem will be a significant concern for the future of high density recording.
The damage in the pinned layer encountered during air bearing surface fabrication may be caused by local temperature elevation of the sensor film due to the friction that occurs while scraping and polishing the ceramic slider material in the air bearing surface fabrication step. Damage may also occur from the spike-like large current generated in the sensor film while scraping the slider material, which applies a large magnetic field to the sensor film.
In the case of a head having a spin valve sensor film using PtMn for the exchange coupling film, it has been known that the damage in the pinned layer is not structural damage caused by diffusion of atoms in the film but damage in view of the magnetic structure since the damage is repaired when heated to 200° C. or higher in a strong magnetic field. However, this method cannot be adopted since exposure to high temperature has other effects such as the pole of the recording head protruding toward the air bearing surface. Therefore, it is difficult to attain higher recording density using the current technology.
Reversal of the magnetic moment in the pinned layer is also caused during air bearing surface fabrication in the existent spin valve type head without the exchange coupling film (disclosed in Patent Documents 2 and 3). In this head type, the reading output is not as greatly decreased as in the head using PtMn for the exchange coupling film as described above. If magnetic bits magnetized in an identical direction are read, there is a problem due to the different positive and negative signal output of the head.